1. Field of the Invention
The present invention relates to an electronic endoscope system, more specifically relates to a lighting device for an electronic endoscope system using more than one rotary shutter, and also a light controller device for such an electronic endoscope system using more than one rotary shutter.
2. Description of the Related Art
In conventional electronic endoscope systems, an endoscopic recording device designed to make an appropriate lighting control possible has been proposed in Japanese laid-open patent publication S62-69222. This endoscopic recording device includes a rotary shutter having a rotational axis the position of which is adjustable relative to an optical axis of a lighting device of the endoscope system; i.e., the distance between the rotational axis and an optical axis of the lighting device is adjustable. The rotary shutter is shaped so that a peripheral speed (peripheral velocity) varies at different points in a radial direction when the rotary shutter rotates (or so that an open area ratio varies at different points on the rotary shutter when the rotary shutter rotates). With the variations in peripheral speed, the amount of light emitted from a light source of the lighting device is adjusted by changing the distance between the axis of the rotational axis and the optical axis of the lighting device.
Although lighting control is possible in the above noted conventional endoscopic recording device disclosed in Japanese laid-open patent publication S62-69222, the structure of the rotary shutter is complicated. Specifically, providing such a conventional endoscopic recording device with a mechanism for changing the distance between the rotational axis and the optical axis of the lighting device is essential, which is costly and troublesome. Additionally, in order to embody this structure, the outer diameter of the rotary shutter has to be several times larger than the diameter of the light bundle of the incident light on the incident end face of a fiber-optic light guide (a bundle of fibers) of the endoscope, which inevitably increases the size of the rotary shutter. On the other hand, if the rotary shutter is formed in an asymmetrical shape with respect to the rotational axis thereof so that an open area ratio changes at different points on the rotary shutter when the rotary shutter rotates, the rotational center of the rotary shutter is not coincident with the center of gravity of the rotary shutter, so that the rotary shutter may lose balance during rotation, and accordingly there is a possibility of the illuminating light which emerges from the exit end face of the fiber-optic light guide becoming unwanted illuminating light, and there is a possibility of the rotary shutter and peripheral components thereof being damaged.